Separation of dinitrobenzene isomers



Patented May 12, 1935 UNITED STATS A'E'NT QFEIQE SEPARATION OF DINITROBENZENE ISOMERS No Drawing. Application July 29, 1935, Serial No. 33,662

'7 Claims.

This invention relates to the purification of meta-dinitrobenzene. It is particularly directed to a method for the separation or removal of isomeric dinitrobenzene from mixtures of metadinitrobenzene therewith.

Meta-dinitrobenzene prepared by the nitration of benzene or nitrobenzene normally contains on the order of 5% to 15% of isomeric dinitrobenzenes (oand p-dinitrobenzene) the presence of which is in many instances undesirable. While it has been proposed to eiiect the purification oi meta-dinitrobenzene by treatment thereof with a caustic alkali or an alkaline salt to form water or alkali-soluble reaction products from the isomers and separation of resultant solution from the solid meta compound, such treatments are not entirely eiiective because of the fact that the alkalis form with the isomeric dinitrobenzenes reaction products which are insoluble in aqueous alkaline solution as well as products which are soluble therein. In consequence a complete purification is not effected.

The present invention is based upon the discovery that by proper control of reaction conditions aqueous sulfite may be caused to react upon the ortho and para dinitrobenzenes in the presence of meta-dinitrobenzene without substantial reaction with the meta-dinitrobenzene and upon the further discovery that such products may be extracted from the meta-dinitrobenzene by means of water or alkaline solutions.

In accordance with the process of the present invention meta-dinitrobenzene in solid phase containing isomers associated therewith is subjected to the action of an aqueous sulfite, for example a Water-soluble sulfite such as an alkalimetal or ammonium sulfite. In this manner substantially complete conversion of the isomers to wateror alkali-soluble products may be effected selectively without any substantial action on the meta-dinitrobenzene.

The duration of the sulfite reaction step may be regulated in accordance with the melting or setting point of the treated dinitrobenzene. Thus ordinary crude meta-dinitrobenzene may melt in the neighborhood of 80 C. As the reaction proceeds, the melting point rises until with substantially complete elimination of isomers the product has a melting point of 89.5 to 905 C. Further action of the sulfite may convert the metadinitrobenzene as well as its isomersto soluble products and accordingly it is desirable to discontinue the treatment as soon as a melting point of about 90 C. is obtained.

It is, of course, desirable that the reaction be carried out with the solid dinitrobenzene in very finely divided form. For obtaining a suspension or dispersion of the dinitrobenzene suitable for treatment in accordance with the present invention, a mixture of the crude dinitrobenzene and 5 water may be heated to a temperature just slightly above the setting point of the dinitrobenzene. By rapid agitation and simultaneous rapid cooling of the liquid, thus causing. the molten dinitrobenzene to solidify, an aqueous dispersion of the 10 compound in the form of very fine crystals may be obtained. These fine crystals make possible intimate contact and a rapid and uniform reaction of the ortho and para compounds with the sulfite treating solution. 15

Suitable sulfites for eiiecting the present purification process are alkali-metal sulfites, for example sodium sulfite, sodium bisulfite, ammonium sulfite, or a sodium ammonium sulfite, or mix- 7 tures of such compounds, for instance sodium sul- 20 fite in admixture with sodium bisulfite, say a sulfite-bisulfite mixture containing from 25% to 60% bisulfite and the balance sulfite. The alkalimetal sulfites have been found to give results superior to those obtained using the ammo 25 nium sulfite and hence are employed in the preferred embodiment of my invention. The solution may be either neutral or alkaline during the purification reaction step. As the reaction proceeds the solution becomes alkaline or more alka- 30 line as a result of the reaction of sulfite with ortho and para dinitrobenzene. Thus at the end of the reaction process the solution normally will be definitely alkaline. This condition is advantageous rather than otherwise since it promotes the solubility of the reaction products which probably are sulfonates or sulfites, the alkali-metal salts of which are especially soluble.

From the foregoing discussion it will be apparent that the entire reaction may be carried out in substantially neutral solution if desired. In such case it is advantageous to Wash the product first with alkaline solution in order to increase the solubility of the reaction products.

The process of this invention may be effected with slurries of dinitrobenzene which contain widely variant amounts of Water. Preferably the process is carried out with slurries which are fiuid enough to be agitated easily and rapidly, and which contain a sufiicient amount of water to hold in solution the quantity of water-soluble sulfite employed and the Water-soluble compounds formed during the treatment. To attain these desirable conditions, it has been found preferable to adjust the amount of water in the reacticn; slurry: of dinitrobenzene :in' aqueous sulfitetwo hours: Theslurry is then cooled to between I I i I 3 solution to between about 145. and about ;5 times C; and C; I :Ihe crystals of, purified meta-i I eated crude; dihijtrobenz enel flinitmbenzene, are separated frorng the: ac'p'iecus e water; may be; replaced: by; :liquidiby filtration, and; are washedfree of wat'ej I other-2 :organic; water-miscible. :sjolubl impurities with cold wateri 1 The result m 1 ff] w" d ing; purified:metaedinitrobenzene is; driedin air; {The sulfite'soiuton reacts-more; rapidly asithe i When; drygi has a melting p'oint ,f 99.6? C and emperatureincreases and I are found that; the. weigh si about ;8l% or E the crude meta i dinitr v ctedficonven ientlyzat tem enzenefrom whichitis derivedi I e ir iti ra t 6f 1 a w e v a s 1" 3 ampie; HI.:-. '100{ parts oft: techn cal: crude eta-jdinitroltenzierfie a sus'p'ended inf l stl p'arts of 1 water and the f suspension is? heated funtilthe :meta-din'itrobenzene is; molte The mi ture is cooled FrapidIyZbeloW SF C.', ahcll5 par 3 of solid "sodium sulfite and: 6 parts :of solid sodium bi'siulfa upo, t e} ortho and para isomers becomesinotice; :abIeEa dthe; losswhicl'r results ircm' thisj zdecom position makes; the use of higher temperature 5 undesirable; It f has been 5 foundthat the treat ment ha s op' umeffectiyenes" v...fi li il l l i:6 or c .o I temperature-the reaction; is-completedi :,j: Th imass. s thenj cooledfio 1 a period offrom; ljtoho urswhen appliedto etween about; 1'0": C.- and :aibou' 3D C: I

sue d meta-i nitrebenzene pro uct be evident theiquantity of: sulfiteit b ts of water; The rigorously is slightly above the melting point of the dinitrobenzene, e. g. about 85 C. The mixture is maintained at that temperature until all the dinitrobenzene is in a liquid state. It is then cooled be- 1 v v v v. s he quarltities of. materials? arated from gthei slurryby ltration' E Y 3 f crystals of unfi a metadinitrobjenzene are 2 Se ifeetz rea en 215cm sufficient to efiect reaction of a substantial proportion of the meta-dinitrobenzene.

3. The method of removing isomeric dinitrobenzene from a meta-dinitrobenzene product low 80 0., say torabout 0., whereby a fine containing the same, which comprises subjectcrystalline dispersion of dinitrobenzene is proing the meta-d nit b n p oduct to the acduced. A previously prepared solution of 60 tion of an aqueous sulfite at a temperature beparts of sodium sulfite (NagSOg) dissolved in 210 tween 45 and 80 C. for a period of time sufparts of water is added quickly to the agitated ficient to efiect reaction of isomeric dinitrobencrystalline dispersion of dinitrobenzene in water. zene but insufficient to efiect reaction of a sub- The resulting mixture is stirred vigorously for a stantial proportion of the meta-dinitrobenzene, period of two hours at a temperature of about and separating the reaction products as an alka- 58 C. to about 63 C. It is then cooled rapidly line solution thereof from the meta-dinitrobento between 10 and 30 C., and the crystals of zene. W purified meta-dinitrobenzene are separated from 4. The method of preparing meta-dinitrobenthe mixture by filtration or other suitable means. zene substantially free from its ortho and para The crystals are Washed with water until they isomers from a meta-dinitrobenzene product are free from water-soluble salts. The washed containing the same, which comprises subjecting 0 meta-dinitrobenzene thus recovered is in the the dinitrobenzene product to the action of an 60 form of fine, faintly yellow crystals, which may aqueous alkali-metal sulfite solution at a tembe dried in any convenient manner. The dry perature between 45 and C. for a. period of meta-dinitrobenzene is very light yellow and has time suflicient to effect reaction of isomeric dinia setting point of 895 to C. The yield of trobenzene but insufficient to effect reaction of a 65 meta-dinitrobenzene is about 85% of the weight substantial proportion of the meta-dinitroben- 65 of crude dinitrobenzene from which it is derived. zene.

Ezcample II. parts of technical crude 5. The method of preparing meta-dinitrobenmeta-dinitrobenzene are suspended in parts zene substantially free from its ortho and para of water. The suspension is heated until the isomers from a meta-dinitrobenzene product 70 meta-dinitrobenzene is molten. It is then cooled containing the same, which comprises subject- 70 rapidly to slightly below 45 C. 15 parts of solid sodium sulfite and 20 parts of solid sodium bisulfite are added quickly. The vigorously stirred mixture is warmed to a temperature between 58 C. and 63C. and held at that temperature for ing the dinitrobenzene product to the action of an aqueous alkali-metal sulfite solution at a temperature between 50 and 80 C. until substantially all of said isomers are dissolved and separating the solution from the meta-dinitrobenzene before a substantial proportion thereof is dissolved.

6. The method of preparing meta-dinitrobenzene substantially free from its ortho and para isomers from a mixture of meta-dinitrobenzene product containing the same, which comprises subjecting the dinitrobenzene product to the action of an aqueous alkali-metal sulfite solution at a temperature between about 58 and about 63 C.

'7. The method of purifying crude commercial dinitrobenzene, which comprises forming a mixture of the crude dinitrobenzene in liquid phase with Water, cooling the mixture below the solidifying point of the dinitrobenzene to produce a fine crystalline slurry thereof and treating the slurry at a temperature between about 58 and about 63 C. with an alkaline sodium sulfite in aqueous solution until the melting point 'of the crystals when dried is approximately 90 C., and thereupon separating the solid crystals from the aqueous solution.

HAROLD W. COWARD. 

